One of the characteristics of the modern cellular network is that the bandwidth thereof is shared among all subscribers within coverage of a particular base station. Therefore, for subscribers in outdoor environments, a bandwidth allocated to each of the subscribers is inversely proportional to the number of effective subscribers in the coverage. Hence, as the number of subscribers of wireless mobile communication networks grows rapidly, burden of outdoor cellular base stations (BSs) becomes increasingly heavier and the bandwidth available to each subscriber becomes increasingly smaller. To solve this problem, many service providers have put great efforts in development of femtocells.
Femtocells are a kind of subminiature low-power base station specially designed for indoor use, and operate in a licensed wireless frequency band, e.g., a frequency band of the Worldwide Interoperability for Microwave Access (WiMAX) network, a frequency band of the Long Term Evolution (LTE) network or a frequency band of the Third Generation (3G) wireless communication network. Since femtocells are simple in structure, cheap in price and easy to install, it is economical to use a femtocell to replace a cellular base station for wireless signal coverage in indoor environments. Furthermore, when a mobile device enters a signal coverage of a femtocell, the cellular base station will be replaced by the femtocell to provide services necessary for the mobile device; this can not only enhance the signal strength in the indoor environments, but also prevent the mobile device from contending for network resources with other mobile devices in the signal coverage of the cellular base station.
Currently in the framework of femtocells, a Closed Subscribers Group mechanism is adopted for access control. In order to verify whether a wireless device can access a femtocell, this mechanism specifies that a verification message must be transmitted through a femtocell, a security gateway, a femtocell gateway all the way to a core network server. However, since the verification message must be transmitted to the core network server for processing in the aforesaid verifying process, the verification duration becomes too long. This gives malicious users an opportunity to disturb normal verification and connection processes of legal subscribers and to occupy the network transmission performance of the femtocell by initiating a denial-of-service attack (bandwidth consumption) simply through repeated log-in attempts.
In view of this, an urgent need exists in the art to provide an access rejection method as well as a femtocell and a femtocell gateway adopting the access rejection method so as to effectively reduce impacts caused by attacks from malicious users.